The Acquired Immunodeficiency Syndrome (AIDS) is characterized by changes in the pool sizes of T cell populations -e.g. depletion of CD4+ cells and naive-phenotype CD4+ and CD8+ cells, expansions of T cell receptor (TCR)-bearing cells of the Vbeta-subfamily or specific for cytomegalovirus (CMV) and HIV-1. Studies of T cell dynamics have generally been based on simple kinetic models assuming a homogeneous pool. Recent advances in methods for measuring T cell kinetics directly in humans have, however, demonstrated the existence of kinetic subpopulations - long lived, short-lived and non-dividing cells - within T cell pools. Our objectives in this project are to characterize further the kinetics of T cell subpopulations in the setting of HIV-1 infection and their relation to HIV-1 immunopathogenesis. Two newly developed in vivo stable isotope labeling techniques will be used: 1) [2H]glucose pulse incorporation/die-away in T cell DNA, to characterize the fraction of memory/effector (m/e)- phenotype CD4+ and CD8+ T cells that survive for greater than 35- 40 days (long-lived or true "memory" cells) compared to those that die-away within 14-21 days (short-lived cells); and 2) long- term administration of 2H2O (deuterated water) for 10-12 weeks, to measure the turnover rates early (short-lived cells) and later (long-lived cells) and the fraction of dividing vs non-dividing (quiescent) cells in the pool. These techniques involve sort- purification of T cell populations and measurement of DNA isotope enrichment by mass spectrometry. Subjects with untreated HIV-1 infection (no antiretroviral [ARV] therapy, CD4 count less than 500 cells/muL, viral RNA greater than 2,500 copies/ml) will be compared to patients with effective long-term ARV therapy (viral RNA less than 50 copies/ml) patients with incomplete viral suppression but improved CD4 counts on a protease inhibitor- containing regimen (viral RNA greater than 2,500 copies/ml, durable CD4 increase greater than 100 cells/muL) and healthy HIV- 1 seronegative subjects. Virologic, immunologic and hormonal factors associated with variations in kinetic subpopulations will be sought. Surface markers that may identify the fate of m/e- phenotype cells as short-lived or long-lived (e.g. CCR-7) will be tested. The kinetic basis of expanded clonally-restricted m/e populations will also be explored, asking whether immunologic memory is maintained by short-lived or long-lived cells in healthy subjects and HIV/AIDS patients. Kinetics will be measured for TCR-Vbeta expansions (sort-purified from screened HIV-positive individuals, in collaboration with Dr. R. Sekaly); anti-CMV, anti-HIV, and anti-Epstein-Barr virus-specific CD8+ T cells (sorted using the Class I HLA-tetramer-peptide technique, in individuals screened for greater than 2 percent prevalence); and anti-CMV-specific CD4+ T cells (sorted by cytokine expression, in collaboration with Drs. L. Picker and V. Maino). The occurrence of "transitional" naive-phenotype proliferation (cells en route to m/e-phenotype) will also be measured, and compared to T cell receptor excision circle (TREC) levels. Finally, the kinetic subpopulation results will be incorporated into computer simulations of the T cell system (in collaboration with Drs. N. Ferguson and R. Anderson, Oxford University). In summary, this project will explore the role of kinetic subpopulations in the expansion and contraction of T cell pools characteristic of HIV-1 infection. Results have potential relevance to HIV-1 pathogenesis and therapy and to vaccination strategies.